North Koreans do not appear to be aware of the death of North Korean leader Kim Jong-un's half brother as Pyongyang has tightened control over the inflow of outside information, sources here said.

But despite the regime's surveillance, it is only a matter of time before the news spreads as more North Korean residents have secret access to outside information, they said.

Kim Jong-nam, the eldest son of late former leader Kim Jong-il, was killed in an airport in Malaysia on Monday after being attacked by two women who are suspected to have used some sort of poison.

It has yet to be confirmed whether North Korea was behind the latest killing, but Seoul's spy agency said Wednesday that Kim Jong-un has issued a "standing order" to murder his sibling after he assumed power in late 2011. North Korea's state media has not shown any reaction to a barrage of reports on the murder.

Many North Koreans neither seem to be aware of Kim's death nor know who Kim Jong-nam is, sources said, in an indication that shows the regime has controlled all information about him.

"I've never heard about that news," said a source who is living in North Korea's provinces bordering China. "Isn't Kim Jong-un the eldest son of late former leader Kim Jong-il?

US-based media Radio Free Asia (RFA) said that North Korean residents including party officials in provincial areas do not know that the half brother of the current leader was killed ahead of the 75th birth anniversary of his late father. But sources said that reports of Kim's death have begun to slowly go viral at the country's border areas with China where access to outside information is relatively easy to come by.

South Korea's military plans to use loudspeakers along the inter-Korean border to inform North Koreans of Kim's killing in a bid to reveal the brutality of the North's regime, government sources said.